﻿using System.Text;

namespace Bread.Utility;

/// <summary> 
/// 获取文件的编码格式 
/// </summary> 
public class TextEncodingDetector
{
    /// <summary> 
    /// 给定文件的路径，读取文件的二进制数据，判断文件的编码类型 
    /// </summary> 
    /// <param name=“path“>文件路径</param> 
    /// <returns>文件的编码类型</returns> 
    public static Encoding Detect(string path)
    {
        FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read);
        Encoding r = GetType(fs);
        fs.Close();
        return r;
    }

    /// <summary> 
    /// 通过给定的文件流，判断文件的编码类型 
    /// </summary> 
    /// <param name=“fs“>文件流</param> 
    /// <returns>文件的编码类型</returns> 
    private static Encoding GetType(FileStream fs)
    {
        byte[] Unicode = new byte[] { 0xFF, 0xFE, 0x41 };
        byte[] UnicodeBIG = new byte[] { 0xFE, 0xFF, 0x00 };
        byte[] UTF8 = new byte[] { 0xEF, 0xBB, 0xBF }; //带BOM 

        Encoding reVal = Encoding.Default;

        BinaryReader r = new BinaryReader(fs, Encoding.Default);
        int i;
        int.TryParse(fs.Length.ToString(), out i);
        byte[] ss = r.ReadBytes(i);
        if (IsUTF8Bytes(ss) || (ss[0] == 0xEF && ss[1] == 0xBB && ss[2] == 0xBF)) {
            reVal = Encoding.UTF8;
        }
        else if (ss[0] == 0xFE && ss[1] == 0xFF && ss[2] == 0x00) {
            reVal = Encoding.BigEndianUnicode;
        }
        else if (ss[0] == 0xFF && ss[1] == 0xFE && ss[2] == 0x41) {
            reVal = Encoding.Unicode;
        }
        r.Close();
        return reVal;

    }

    /// <summary> 
    /// 判断是否是不带 BOM 的 UTF8 格式 
    /// </summary> 
    /// <param name=“data“></param> 
    /// <returns></returns> 
    private static bool IsUTF8Bytes(byte[] data)
    {
        int charByteCounter = 1; //计算当前正分析的字符应还有的字节数 
        byte curByte; //当前分析的字节. 
        for (int i = 0; i < data.Length; i++) {
            curByte = data[i];
            if (charByteCounter == 1) {
                if (curByte >= 0x80) {
                    //判断当前 
                    while (((curByte <<= 1) & 0x80) != 0) {
                        charByteCounter++;
                    }
                    //标记位首位若为非0 则至少以2个1开始 如:110XXXXX...........1111110X 
                    if (charByteCounter == 1 || charByteCounter > 6) {
                        return false;
                    }
                }
            }
            else {
                //若是UTF-8 此时第一位必须为1 
                if ((curByte & 0xC0) != 0x80) {
                    return false;
                }
                charByteCounter--;
            }
        }
        if (charByteCounter > 1) {
            throw new Exception("非预期的byte格式");
        }
        return true;
    }

}